1. Field of the Invention
The present invention relates to a tool trajectory display device having a function for displaying an inversion position of a servo axis.
2. Description of the Related Art
Generally, in a machine tool wherein processing is carried out by an interpolating operation due to a plurality of servo axes, it is likely that a shape error between a commanded shape and a processed shape may increase at an inversion position where the polarity (or sign) of each axis is inverted. As a factor thereof, mechanical play (for example, a backlash in a ball screw), and a delay in response of a servo due to a change in a direction of friction, etc., can be cited. In such a case, the shape error may be decreased by correcting the position and/or acceleration of each axis, and by performing servo adjustment such as gain adjustment.
For example, Japanese Unexamined Patent Publication (Kokai) No. 2004-021954 discloses a method for displaying a tool trajectory of NC data for processing a workpiece by using micro line segments of three (X, Y and Z) axes, wherein the tool trajectory is displayed as a set of the line segments or end points of the line segments. Concretely, this document describes that an inclination (plus, minus or zero) of each line segment relative to a specified axis is judged, and then a display attribute of the line segment is changed depending on the result of judgment, whereby a concave or convex shape in the tool trajectory can be easily determined.
Further, Japanese Unexamined Patent Publication (Kokai) No. 2011-170584 discloses a numerical controller, wherein a coordinate of a tool center point is calculated from a coordinate of each drive axis at each time point, a tool radius correction vector extending between the tool center point and an actual machining point is determined, a coordinate of the actual machining point is calculated, and a trajectory of the actual machining point is displayed.
In the prior art, in a machine tool constituted by only linear axes, it is easy to associate the inversion position of each axis with the processed shape. However, in a machine tool including a rotation axis, such as a five-axis machine tool, it is not easy to do so. Therefore, it is difficult to properly adjust a servo since it cannot be clearly determined whether the shape error depends on the inversion motion of the servo axis or the other factor.
For example, in Japanese Unexamined Patent Publication (Kokai) No. 2004-021954, a tool trajectory is displayed based on NC data generated by a CAD/CAM. However, since a commanded trajectory of the NC and an actual trajectory of the tool center point are not displayed, the proper servo adjustment cannot be carried out. Further, in a constitution having two or more axes including a rotation axis, coordinate conversion is necessary to represent a coordinate of the tool center point in a coordinate system of three linear axes (X, Y and Z). Since a plurality of variables relate to components of X, Y and Z axes after the coordinate conversion, the inversion point of each axis cannot be found based on inclinations of the three-axis micro line segments of X, Y and Z relative to the specified axis.
On the other hand, in Japanese Unexamined Patent Publication (Kokai) No. 2011-170584, although a trajectory of actual process points can be displayed by taking the tool radius correction vector into consideration, the inversion position of each axis is not displayed on the tool trajectory. Therefore, it is difficult to clearly determine whether the shape error depends on a change in the polarity of the servo axis or another factor.